The present invention is directed to a mechanism for making photographic exposures on a strip-shaped light-sensitive material. The mechanism includes an image-field limiting frame that encloses a light-path opening and means for guiding the strip-shaped light-sensitive material behind the image field limiting frame and the light path opening. The mechanism further includes a transport arrangement for the forward transport of the strip-shaped material in its longitudinal direction and at least one mask that can be brought into and out of use for the purpose of covering portions of the light-path opening thereby forming a smaller picture window. The portions of the light-path opening coverable by the mask adjoin the edges of the light-path opening that are at right angles to the longitudinal direction of the strip-shaped material. Thus, through displacement of the mask, the first edge of the image window seen in the forward transport direction of the strip-shaped material, as well as the second edge of the image window, are changable in their position. The mechanism also includes control means for the automatic limitation of the forward transport steps for the strip-shaped material by the transport arrangement which is proportional to the picture window left open by the mask.
Known mechanisms of the above mentioned type are each arranged as integratable parts of a photographic camera and enable, with one and the same camera, to make photographic exposures with two different picture formats. In such cameras, the choice of the desired picture format must be made each time prior to the introduction of the strip-shaped light-sensitive material and can then no longer be changed. Coincidental with the choice of the picture format, the transport arrangement must be switched or partially exchanged each time in order to adapt the transport step of the light-sensitive material that is required after each exposure to the selected picture format. In the simplest case, a mask is introduced in the view area limiting frame that reduces the view window, or the mask must be removed, and the transport steps of the strip-shaped material must be manually executed and measured by means of numbers of two different number series printed on the back of the material which are visible through two alternatively exposable indicator windows. In the viewer of the camera, fields corresponding to the two picture formats are simultaneously visible which therefore does not exclude mistakes.
For universal cameras, interchangable film cassettes with different sized picture windows are also known. Each film cassette has its own transport arrangement for the film with a constant transport step corresponding to the fixed picture window of the cassette. If at least two such cassettes with different picture windows are available, the picture format can be selected for each exposure corresponding to the given possibilities by exchanging the cassettes. This solution results in a relatively great material expenditure.
Also known are microfilm exposure instruments in which the size of the picture window is changeable in the longitudinal direction of the light-sensitive strip-shaped material and the transport step of the transport arrangement is automatically adapted to the set picture window size. In these known instruments, for the purpose of avoiding the overlapping of sequential photographic pictures, it is a necessity in each case to first change the size of the picture window and then subsequently to transport the strip-shaped material forward to exposure location except in the case where the second edge of the picture opening, seen in the forward transport direction of the strip-shaped material, has an unchanged position. In many applications, the latter is, however, detrimental since when the size of the picture window is changed, the center of the window is displaced coincidentally in relation to the optical axis of the objective. Such a displacement may be tolerable in the microfilm exposure of documents, but is generally not acceptable in a camera for general photography purposes.